1. Field of the Invention
The present invention relates to an apparatus for classifying and purifying fine particles to obtain only the desired superconductor particles form among a mixtures of fine particles of different particle diameters comprised of superconductors, normal conductors, insulators or the like having different critical temperatures, critical magnetic fields, etc.
2. Related Background Art
In recent years, it has been discovered that the sintering of ceramic materials with certain definite composition can give a sinter that exhibits superconductivity (or superconducting) at 77 K. or more, or, in some instances, near room temperature. However, the crystal structure and the phase of these superconductors have not been sufficiently elucidated yet, and usually there coexist non-superconducting crystal phases.
In the instance where the non-superconducting crystal phases coexist, it is very difficult to separate them from the superconducting crystal phases. Moreover, no technique has been established that will form only the superconducting crystalline material by controlling heat-treatment conditions. In recently available ceramic superconductors, there also often coexist a plurality of superconducting crystal phases different in the critical temperature or critical magnetic field, and no method has been established to separate only the superconducting crystal phases having any desired critical temperature range and critical magnetic field range from among them.
In addition, the sinter having superconductivity usually comprises amass or aggregate of fine crystals, and its superconductivity characteristics depend greatly on the state of crystal grain boundaries so that its crystal grain boundaries must be made uniform to obtain a sinter having stable characteristics.
A proposal has never been made to obtain a superconducting sinter having uniform crystal grain boundaries by re-sintering superconductor fine particles having uniform particle diameter. However, any suitable method for classifying such superconductor fine particles having uniform particle diameters has not been discovered, and nothing has been available except for the method in which the generally practiced particle classification methods as described in Funtai Kogaku Handobukku (Particle Technology Handbook) (edited by Koichi Iitani, Asakura Publishing Co.) are applied in the superconductor fine particles.
Known as the conventional generally practiced particle classification methods are a screening method in which sieves having different openings are piled up in the order from those having larger opening diameter to carry out classification, a sedimentation method in which the terminal settling velocity of the particles settling in a fluid is utilized to carry out the classification, and similar methods.
For example, however, in the screening method, it is impossible to prepare those having a screen opening of several micrometers or less, thus preventing classification for particles of very small diameter. Moreover, it is often practiced to apply pressure loading to the fine particles to force them to pass through the screen openings, and in such an instance the problems occur such that the classification cannot be carried out in vacuo as a means for classification with higher precision. Also, in the sedimentation method, where the settling velocity depends not only on the diameter of particles but also the specific gravity thereof, no strict classification can be carried out. In instances where a liquid phase sedimentation method is used, it requires a lot of labor to separate fine particles from liquid, and also the settling velocity is so low in general as to take much time for the classification. This method also involves the problems such that it cannot naturally be carried out in vacuo.